Project Summary/Abstract The proposed research will use data from the Medical Expenditure Panel Survey to investigate the impacts of the Affordable Care Act (ACA) on the health care utilization of non-elderly adults. The research will utilize the identification strategy developed by the proposal's investigators in a previous study that estimated the causal effects of the ACA on health insurance coverage in both Medicaid expansion and non-expansion states (Journal of Policy Analysis and Management, forthcoming). This strategy features a difference-in-difference-in-differences model with the differences coming from time, state Medicaid expansion status, and local area pre-treatment uninsured rate. This last source of variation, which arises because universal coverage initiatives provide the most intense treatments in areas with high baseline uninsured rates, allows us to disentangle the causal effect of the ACA from the underlying time trend while also accounting for the possible endogeneity of state Medicaid expansion decisions. The proposed research will move past estimating impacts on health insurance outcomes to also examine numerous outcomes related to health care utilization. These outcomes will include frequency of and expenditures on: physician and non-physician office visits; inpatient, outpatient, and emergency room hospital visits; and prescription drugs. We will also examine total medical expenditures from all categories. For the expenditure outcomes, we will further subdivide by payer, including out-of-pocket, private insurance, and Medicaid. We will also conduct subsample analyses by age, race/ethnicity, education, income, gender, marital status, and presence of children in the home. Using these results, we will compute the extent to which the ACA reduced disparities on the bases of race/ethnicity and socio- economic status in both Medicaid expansion and non-expansion states. Finally, we will estimate instrumental variables models to determine the impacts of private coverage and Medicaid coverage on the various outcomes.